Insertion machines are used for positioning electronic components on a printed circuit board. The electronic components are arranged on a transport tape consisting of cardboard or plastic material, and they are covered by another tape. The transport tape is wound into a roll and inserted in a feeder. The transport tape has holes on at least one side thereof, said holes being engaged by a pin wheel which is driven by a drive motor and which thus moves the transport tape. The cover sheet is peeled off simultaneously so that the electronic components are exposed. The electronic components are positioned precisely at a transfer location by means of the pin wheel, removed by a vacuum pipette and placed onto the printed circuit board.
Since the electronic components become increasingly smaller in size and since the number of electronic components on a printed circuit board increases continuously, modern insertion machines must offer space for the highest possible number of feeder devices with transport tapes carrying the electronic components. In order to save space, the individual feeder devices must be as narrow as possible.
It is known to use slim motors as drive motors whose axles extend parallel to the side walls of the feeder device. Hence, such a conventional cylindrical drive must have a very small diameter, i.e. the torque that can be generated by said cylindrical drive will only be very low and, consequently, a high gear reduction will be necessary.
It is also known to use flat motors as drive motors whose axles extend perpendicular to the side walls of the feeder device. These flat motors of the internal- or external-rotor type are able to provide a substantially higher torque on the basis of a small overall height.
Such a feeder device is known e.g. from European patent EP 0 897 258 B1. This patent specification describes a feeder device comprising a tape feeding unit which is secured to a main frame and which is driven by an electric motor that is secured to said main frame as well. The tape feeding unit advances the transport tape with the electronic components while the cover sheet is removed simultaneously. At a transfer position, an electronic component is sucked up by a vacuum pipette and placed onto a printed circuit board. The drive motor is preferably a pulse motor through which the electronic components on the transport tape can be positioned precisely at the transfer position. This can be accomplished e.g. by varying the number of pulses or the pulse duration of the pulse motor.
Also the German patent application DE 101 57 230 A1 describes a feeder device for an insertion machine. The feeder device comprises a main frame having arranged thereon a transport tape feeding unit, a separator in which the cover sheet is separated from the transport tape and a recovery unit in which the cover sheet is wound up. The feeding unit, the separator and the recovery unit are driven via a disk element which is fixedly attached to one side of the main frame and which has arranged thereon a plurality of armature coils. A shaft is rotatably supported in the middle of this first disk element. The shaft has secured thereto a second disk element which is connected to a circular permanent magnet means. Due to the interaction between the permanent magnet means and the armature coils, the shaft is rotated. The rotary movement is transmitted to the feeding unit, the separator and the recovery unit.
Another feeder device for an insertion machine is disclosed in U.S. Pat. No. 6,379,098 B1. The feeder device comprises a first drive motor for advancing the transport tape and a second drive motor which drives a mechanism for peeling the cover sheet off from the transport tape. The first drive motor includes a cylindrical stator which is fixedly secured to the frame of the feeder device. A hollow cylindrical rotor surrounds the stator whereby an air gap is formed between the rotor and the stator. The rotor includes a hollow cylindrical permanent magnet with a gear formed at the back of said permanent magnet. This gear meshes with four additional gears by means of which the rotor is held in position.
These feeder devices known from the prior art are disadvantageous insofar as the thickness of the feeder devices is determined by the length of the drive motors as well as by the thickness of the housing walls of the motor and of the feeder device. In the case of the feeder device described in U.S. Pat. No. 6,379,098 B1 attempts are made to remedy this drawback by providing a shaftless drive motor and by supporting the rotor by means of four gears. This makes the assembly of the system comparatively complex.